Following traumatic brain injury (TBI), the immature rat brain experiences many secondary insults that lead to delayed cell death. Although considerable evidence indicates that mitochondria are primary mediators of ischemic and excitotoxic neural cell death and survival, relatively little is known regarding mitochondrial involvement in adult TBI, and nothing has been reported for models of pediatric TBI. Limited studies of the immature rat brain have demonstrated vulnerability to many known mediators of mitochondrial injury, including elevated intracellular calcium and oxidative stress. Mitochondrial alterations can also trigger the cascade of caspase activities that mediate apoptosis, a process of programmed cell death that appears particularly important in TBI. The working hypothesis for the proposed study is that the response of brain mitochondria to metabolic acidosis, elevated calcium, oxidative stress, and pro-apoptotic proteins plays an integral role in the neurochemical, histologic, and neurologic outcome following pediatric TBI. We will test the following mechanistic hypotheses using a clinically relevant model of pediatric TBI: 1) Mitochondrial injury early after TBI increases the sensitivity of mitochondria to cellular factors that promote apoptotic or necrotic cell death cascades. 2) Cerebral lactic acidosis after TBI promotes cytochrome c release, mediated by mitochondrial swelling due to activation of the membrane permeability transition. 3) Oxidative stress following TBI contributes to mitochondrial dysfunction, cell death and neurologic injury. This study will help define the molecular mechanisms by which mitochondria are injured after TBI in immature animals. This may identify novel targets for neuroprotection following TBI in infants and children. This proposal is intended to provide for the research experience and career development of the applicant, specifically involving the mechanisms of, and therapeutic strategies for, the treatment of acute brain injury. The Departments of Anesthesiology and Pediatrics, and the Brain Injury and Neuroprotection Research Group at the University of Maryland will provide a rich environment for the study of experimental brain injury, and have a strong commitment to fostering meaningful and contemporary research in this field.